In the first movie he commits extrajudicial killings (maybe these are murders, maybe not) and then when leaving the scene almost kills a 'friendly' pilot, while laughing about it all with his buddy.
I'm Civil War he tries to kill the man who murdered his parents, for revenge, not justice.
And when Stark almost killed thr world through Ultron, after being traumatised by near death experience saving NYC, he continued his self righteousness and ran straight for the Sarcovia Accords as a counter balance.
If you look at the Avengers from a realistic perspective then they're a group of anarchistic, unhinged, uncontrollable vigilantes who resist any kind of oversight or procedures to reduce collateral damage.
They possesses supernatural abilities and incredible technologies and use them to... maintain American hegemony and the capitalist status quo. It's almost some Elysium type shit.
